In any of these cases i tried with:
QString("password")
"password"
password

Since I had no idea what was(is) going on, I tried also:2a- Adding gradually missing in password argument-1 position until the 15th argument, ex:
Open(filename,password)
Open(filename,missing,password) and so on2b- Fixxed password on the fifth and tried to input random data in other arguments